Curcumin induced photodynamic therapy mediated suppression of quorum sensing pathway of Pseudomonas aeruginosa: An approach to inhibit biofilm in vitro

Objective: The objective of this study was to inhibit the Pseudomonas aeruginosa biofilm through curcumin-mediated antimicrobial photodynamic therapy (A-PDT). Background: The mechanism behind A-PDT mediated photoinactivation depend upon reactive oxygen species (ROS) production, like singlet oxygen and free radicals. Methods: To evaluate the antibacterial efficacy of curcumin induced A-PDT on P. aeruginosa by colony forming unit (CFU) while antibiofilm action was determined by the use of crystal violet, XTT, congored binding assay and confocal laser scanning microscope (CLSM). Results: We found that curcumin with 10 J/cm(2) of light reduces P. aeruginosa biofilm more efficiently than without light. Extracellular polymeric substances (EPS) production was also reduced by approx 94 % with 10 J/cm(2) of light dose. CLSM images showed that the thickness of biofilms were reduced from > 30 mu m to < 5 after treatment with curcumin followed by 10 J/cm(2) of light irradiation. Curcumin showed better bacteriostatic activity than bactericidal activity. Singlet oxygen is primarily responsible for photo-damage and cytotoxic reactions caused by curcumin-mediated APDT. Genes involved in quorum sensing (QS) pathway was also found to be inhibited after APDT. Curcumin with 5 J/cm(2) light inhibits QS genes and on increasing light dose i.e10 J/cm(2), we found a drastic reduction in gene expression. Conclusion: We conclude that the curcumin mediated A-PDT inhibits biofilm formation of P. aeruginosa through QS pathway by the action of singlet oxygen generation which in turn reduced EPS of the biofilm.